Catalytic oxidation of propylene to acrolein on a multicomponent oxide catalyst

Rate equations have been found and reaction schemes for oxidation of propylene to acrolein and acrylic acid have been suggested.

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Bond energy of surface oxygen in multicomponent oxide catalysts for propylene oxidation to acrolein

Bond energy of surface oxygen for the multicomponent oxide catalyst Mo₁₂Bi₁Ni_2.5Fe₃Co_4.5K_0.07P₁/SiO₂ has been measured in conditions of propylene oxidation and found to be 272 kJ/mol.

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Mo₁₂Bi₁Ni_2,5Fe₃Co_4,5K_0.07P₁/SiO₂, , 272 /.

     

Changes in the catalytic properties of a multicomponent molybdenum catalyst under vibro-fluidized catalyst bed conditions

Activation effect of oxidative dehydrogenation of butene-l on a multicomponent molybdenum catalyst at various temperatures has been studied by pulse and flow techniques. It is shown that under vibrofluidization not only reactive but also adsorption properties of the catalyst surface change. Oxygen consumption in the reaction process has been examined.

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-1 . , , . .

     

Investigation of propylene oxidation on multicomponent a Bi-and Mo-based oxide catalyst

It has been established that porpylene oxidation to acrolein on a multicomponent oxide catalyst containing Mo, Bi, Fe, Ni, Co, K, P and SiO₂ follows an alternating oxidation-reduction mechanism and involves the participation of lattice oxygen with the bond energy of about 280 kJ/mol.

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, Mo, Bi, Fe, Ni, Co, K, P SiO₂ 280 /.

     

Kinetics of propylene oxidation to acrolein on an Fe?Sb oxide catalyst

The kinetics of propylene oxidation to acrolein and CO₂ on a Fe–Sb oxide catalyst have been studied in an integral reactor. A satisfactory rate equation has been derived with the assumption of a linear dependence of the activation energy and heats of adsorption of oxygen and water on the degree of reduction of the catalyst.

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CO₂ Fe–Sb . , .

     

A new method to obtain supported oriented oxides: MoO3 graphite catalyst in propylene oxidation to acrolein

Oriented MoO₃-graphite catalysts were prepared by oxyhydrolysis of a MoCl₅-graphite intercalation compound and used in catalytic oxidation of propylene. Results show a correlation between the building of specific crystal faces of MoO₃ and a selectivity towards acrolein formation.

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MoO₃- -MoCl₅- - . MoO, - .

     

Study of the mobility of lattice oxygen in complex oxide catalysts for partial oxidation of propylene to acrolein

The amount of oxygen in the lattice of solids that participates in the elementary stages of partial propylene oxidation is determined for two types of Co-Mo-Bi-Fe-Sb-K-O catalysts (I, II) differing in the method of introduction of antimony and potassium. Two independent methods are used: (1) on the basis of the yield of the oxygen-containing products of propylene oxidation by oxygen of the catalyst in a pulse regime and (2) with the use of Möessbauer spectroscopy. Coincidence of the results obtained by both methods indicates that the active oxygen of the catalyst lattice is formed during redox transformations of iron(III) molybdate entering the composition of the catalysts. Data on the reduction of the catalysts in a pulse regime at various temperatures, which were processed in the framework of the diffusion model, allowed the estimation of the rate constants for diffusion of the lattice oxygen. An increase in the mobility of the lattice oxygen in catalyst I, which is modified with a small amount of antimony as compared to catalyst II, results in an increase in the overall productivity of the sample and in a decrease in the selectivity of propylene oxidation to acrolein. This correlates with the increase in the total amount of the lattice oxygen participating in the process.     

Catalytic oxidation of acrolein to acrylic acid over a molybdenum-vanadium catalyst

By the method of gas chromatography it has been found that the adsorption of acrolein takes place without dissociation whereas acrylic acid is adsorbed dissociatively. The adsorption of water vapor proceeds also dissociatively and results in increasing the number of the Brönsted acid centers. The presence of water vapor has a positive effect on the desorption rate of acrylic acid and a negative effect on the reoxidation rate of the catalyst.

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, , . , . , — .

     

Study of the steps of acrolein oxidation over a vanadium-molybdenum catalyst

Acrolein is oxidized to acrylic acid over a V–Mo catalyst by lattice oxygen, while the formation of CO₂ also involves gas phase oxygen. The steady state of catalyst reduction is about 5% monolayer and is characterized by an oxygen binding energy of 61 kcal/mol.

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V–Mo- , CO₂ . 5% 61 /.

     

Paths of carbon dioxide formation in isobutylene oxidation over A Sn-Sb-O catalyst

It has been shown that in the process of isobutylene oxidation over a tinantimony oxide catalyst, carbon dioxide is formed 1) directly from isobutylene, 2) via the oxidation of methacrolein and 3) via burning of the condensation products deposited on the catalyst surface.

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, - : 1) , 2) , 3) , .

     

IR-spectroscopic studies of the interaction of propylene and acrolein with a CoMoO4 catalyst

IR spectra of propylene and acrolein adsorbed at different temperatures on CoMoO₄ supported on MgO were recorded. Four different surface species were found: a -complex, an oxygen bonded carbonyl complex, acrylic acid and a carboxylate type complex. The mechanism of their transoformation is discussed.

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- CoMoO₄ MgO. , 4 : -, , , . .

     

Formation of the active component of a vanadium-molybdenum oxide catalyst in acrolein oxidation

An acrolein-containing reaction mixture reduces V⁵⁺ to V⁴⁺, accompanied by decomposition of the ammonium salt of vanadium-molybdenum-silicon heteropolyacid (HPA) to form a compound with the tentative composition of VMo₃O_11+x, which is the active component of the catalyst.

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V⁵⁺ V⁴⁺, VMo₃O_II+X, .

     

Kinetics of isobutylene oxidation on a Mo-Sb-Te-O (1 : 0.6 : 0.06) catalyst

Kinetics of isobutylene oxidation over a Mo-Sb-Te-O catalyst is studied in a flow-circulation system with the Korneichuk differential reactor. The reaction orders of methacrolein, acetic acid, acetone, and CO₂ formation, as well as the order of the overall reaction of isobutylene oxidation into methacrolein, with respect to oxygen and isobutylene are determined at 613–703 K and oxygen concentrations of (0.33–13.05) x 10⁻³ mol/1 and isobutylene (3.2–121.9) × 10⁻⁴ mol/1. The activation energies of these reactions are determined.     

Oxidation of propylene and isobutylene in a reactor with barrier discharge

The oxidation of propylene and isobutylene in barrier-discharge plasma in the presence of octane was studied. The possible reaction mechanism was considered.Translated from Zhurnal Prikladnoi Khimii, Vol. 77, No. 11, 2004, pp. 1922–1924.Original Russian Text Copyright © 2004 by Kudryashov, Ryabov, Sirotkina, Shchegoleva.     

Nanocrystalline cobalt oxide: a catalyst for selective alkane oxidation under ambient conditions

Nanocrystalline cobalt oxide activates propane, yielding propene at room temperature and pressure.     

Partial oxidation of propylene to propylene oxide over a neutral gold trimer in the gas phase: a density functional theory study

We report a B3LYP study of a novel mechanism for propylene epoxidation using H(2) and O(2) on a neutral Au(3) cluster, including full thermodynamics and pre-exponential factors. A side-on O(2) adsorption on Au(3) is followed by dissociative addition of H(2) across one of the Au-O bonds (DeltaE(act) = 2.2 kcal/mol), forming a hydroperoxy intermediate (OOH) and a lone H atom situated on the Au(3) cluster. The more electrophilic O atom (proximal to the Au) of the Au-OOH group attacks the C=C of an approaching propylene to form propylene oxide (PO) with an activation barrier of 19.6 kcal/mol. We predict the PO desorption energy from the Au(3) cluster with residual OH and H to be 11.5 kcal/mol. The catalytic cycle can be closed in two different ways. In the first subpathway, OH and H, hosted by the same terminal Au atom, combine to form water (DeltaE(act) = 26.5 kcal/mol). We attribute rather a high activation barrier of this step to the breaking of the partial bond between the H atom and the central Au atom in the transition state. Upon water desorption (DeltaE(des) = 9.9 kcal/mol), the Au(3) is regenerated (closure). In the second subpathway, H(2) is added across the Au-OH bond to form water and another Au-H bond (DeltaE(act) = 22.6 kcal/mol). Water spontaneously desorbs to form an obtuse angle Au(3) dihydride, with one H atom on the terminal Au atom and the other bridging the same terminal Au atom and the central Au atom. A slightly activated rearrangement to a symmetric triangular Au(3) intermediate with two equivalent Au-H bonds, addition of O(2) into the Au-H bond, and rotation reforms the hydroperoxy intermediate in the main cycle. On the basis of the DeltaG(act), which contains contribution from both pre-exponetial factor and activation energy, we identify the propylene epoxidation step as the actual rate-determining step (RDS) in both the pathways. The activation barrier of the RDS (epoxidation step: DeltaE(act) = 19.6 kcal/mol) is in the same range as that in the published computationally investigated olefin epoxidation mechanisms involving Ti sites (without Au involved) indicating that isolated Au clusters and possibly Au clusters on non-Ti supports can be active for gas-phase partial oxidation, even though cooperative mechanisms involving Au clusters/Ti-based-supports may be favored.     

Catalytic partial oxidation of methane to synthesis gas over a ruthenium catalyst: the role of the oxidation state

The catalytic partial oxidation of methane to synthesis gas over ruthenium catalysts was investigated by thermogravimetry coupled with infrared spectroscopy (TGA-FTIR) and in situ X-ray absorption spectroscopy (XAS). It was found that the oxidation state of the catalyst influences the product formation. On oxidized ruthenium sites, carbon dioxide was formed. The reduced catalyst yielded carbon monoxide as a product. The influence of the temperature was also investigated. At temperatures below the ignition point of the reaction, the catalyst was in an oxidized state. At temperatures above the ignition point, the catalyst was reduced. This was also confirmed by the in situ XAS spectroscopy. The results indicate that both a direct reaction mechanism as well as a combustion-reforming mechanism can occur. The importance of knowing the oxidation state of the surface is discussed and a method to determine it under reaction conditions is presented.     

低浓度煤层气在发烟硫酸中液相部分氧化的催化剂研究

在发烟硫酸溶液中,对低浓度煤层气液相部分氧化的催化剂进行了筛选,考察了硫酸盐化合物系列、过渡金属化合物系列、碘化合物系列对低浓度煤层气液相部分氧化的催化活性,对筛选出的碘催化剂进行了催化剂加入量的考察,并对碘催化剂的催化机理进行了讨论。结果表明,碘单质的催化效果最好,低浓度煤层气中甲烷转化率可达79.69%,甲烷选择性可达83.74%。在对碘催化剂加入量的考察中发现,随着碘催化剂加入量的增加,低浓度煤层气的转化率先增加,达到最大值以后,再逐渐减小。根据甲烷在发烟硫酸溶液中液相部分氧化的反应机理,提出低浓度煤层气在发烟硫酸溶液中液相部分氧化的反应机理属于亲电反应机理。     

Mukaiyama-Michael reactions with acrolein and methacrolein: a catalytic enantioselective synthesis of the C17-C28 fragment of pectenotoxins

Enantioselective iminium-catalyzed reactions with acrolein and methacrolein are rare. A catalytic enantioselective Mukaiyama-Michael reaction that readily accepts acrolein or methacrolein as substrates, affording the products in good yields and 91-97% ee, is presented. As an application of the methodology, an enantioselective route to the key C17-C28 segment of the pectenotoxin using the Mukaiyama-Michael reaction as the key step is described.